Subscription television system



0t- 20, 1959 G. v. MORRIS ETAL 2,909,592

SUBSCRIPTION TELEVISION SYSTEM 5 Sheets-Sheet 1 Filed April l5. 1953 A B B' Oct. 20. 1959 Filed April 15, 1953 G.. v.fMoRRls ETAL 2,909,592

SUBSCRIPTION TELEVISION SYSTEM 5 Sheet/sv-Sheet 2 GEORGE V. MORRIS ERwlN M. Rossi-IKE JNVENToRs.

THEIR ATTORNEY.

G. V. MORRIS ETAL SUBSCRIPTION TELEVISION SYSTEM ou, 2o, 1959 Filed April 15, 1.953

5 Sheets-Sheet 5 Um nu @una mom W25 mow GEORGE V. MORRIS ERWIN M. ROSGHKE INVENTORS.

B THEIR ATTORNEY.

G. v. MORRIS la'rAl.4 2,909,592

SUBSCRIPTION TELEVISION SYSTEM 5 Sheets-Sheet 4 Oct. 20, 1959 Filed-April 15. 195s G. V. MORRIS ETAL SUBSCRIPTION TELEVISION SYSTEM 5 Sheets-Sheet 5 QOOOOIOOIO IIOIIOOIUI l-i" IN VEN TORS GEORGE V. MORRIS ERWIN NLROSCHKE THEIR ATTORNEY.

DOO@ Oct. 20, 1959 Filed April 15, 195s United States Patent OA y Y 2,909,592 Y SUBSCRIPTION IELEvIsIoN SYSTEM George V. Morris, Chicago, and Erwin MIRoschke,

Des Plaines, Ill., assignors to Zenith Radio Corporation, a corporation of Delaware Application April 1s, 195s, serial No. 349,016

1o claims. (cl. 17a- 5.1)

This invention relates to subscription television apparatus and more particularly to an improved method for providing coding and decoding information in such a system. Since the invention may be practiced in either a transmitter or receiver, the term encoding is used herein in its generic sense -to encompass either coding at the transmitter or decoding at the receiver.

A number of subscription television systems have been proposed; usually they are characterized by the fact that the radiated Vtelevisionsignal is coded in accordance with a coding schedule, which may be repetitiveorrandom, and decoding information is made -available to subscribers to control decoding apparatus in their receivers in order to permit utilizationof the coded telecast. For example, in U.S. Patent No. 2,510,046 issued May 30, 1950, in the name of Alexander Ellett et al. and assigned to the present assignee, the decoding information or a key signal is preferably transmitted to subscriber receivers by a closed conductive network and a Very high degree of secrecy is thus attained. The wire facilities which may be employed may, of course, be existing networks such as those of telephone and power utilities but such utilities must be compensated for the service rendered. j Further, some vowners of television receivers who may be desirous of utilizing the transmitted information from the subscription television station may be without telephone service or may be on power lines not accessible`to the power system over which the key signal is to be `disseminated from the subscription transmitter.' j

With those problems in mind inventions have been made, for example, as disclosed in application Serial No. 281,418, filed April 9, 1952, issued July 15, 1958, as Patent No. 2,843,646, in the Vname of George V. Morris et al. and assigned to the present assignee, directed towards disseminating the key information by an airborne signal. This method of. distribution presents the problem of preventing non-subscribers from extracting the decoding information from the air-borne signals and utilizing it in the unauthorized decoding of the subscription program. The ultimate goal in such systems, featuring air-borne distribution of decoding data, is maximum secrecy -Witha minimum of complexity. in the transmitting and receiving equipment., That goal`has been approached in the invention described and claimed in copending application Serial No. 326,107 liled in the name of Jack E; Bridges onV December 15, 1952, issued February 1l, 1958, as Patent No. 2,823,252, and assigned to the assignee of the present application. In the Bridges system, signals from a combination of a plurality of randomly energized signal generators having different operating frequencies is passed through a transposition mechanism for selective application to a series of input circuits of a bistable code actuator which establishes an operating mode in the transmitter determined by the applied signals. The transposition mechanism includes a plurality of switches which may be adjusted to any one of a number of operating positions to control the operating mode that a given combination of applied signals .ICC

may otherwise impose on thetransmitter. Complementary apparatus controls the actuator of the decoder in subscribers receivers to which the same combinationY of signals, received asa radiation component during the subscription program, maybe applied to effect decoding of the telecast which has been coded by the mode changes introduced at the transmitter. It is desirable from a merchandising standpoint to reduce the number of operations or adjustments to be performed by subscribers to minimize the` possibilities of error which may cause the subscriber to miss vthe program which he desires to receive.

It is an object of this invention to provide a relatively simple but secure coded subscription television system.

It is a further object of 4this invention to provide a simple and convenient method for `prescribing coding and decoding information in a subscription television system. v v r Y It is still another object of this invention -toV provide an easilymerchandisable element which may be applied at subscription television transmitters and receivers for controlling the coding and decoding of the subscription television signal while posing to non-subscribers great difficulty in duplicating Vthe element, thus providing a high degree of security for the subscription system.

In accordance with the present invention, a subscription television system comprises an encoding mechanism having a plurality of, operating conditions eachof which imposes a different operating mode upon the system and the mechanism is responsive to applied signals to shift from one such operating condition to anotherQ There are means in the system for deriving at least one primary encoding signal and a transposer is'coupled between the signal-deriving means and the encoding mechanism for determining the response of that mechanism to the primary signal. The transposer includes at least onev primary element and at least onesecondary element normally having a predetermined circuit relationship with respect to one another and establishing a preselected response of the encoding mechanism to the primary signal. A transposing element is removably disposed'in functional relation with respect to the transposer and translated by the transposer to the encoding mechanism,

establishes a preselected 'response of that mechanismV to the applied signal.

The features of this invention which are believed to be novel are set forthwith particularity in the appended claims. The organization and manner of operation of the invention itself, together with further objects andadvantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: Y Figure 1 represents one portion of a subscription television transmitter constructed in accordance with vthe present invention; l Y

Figure 2 represents the remaining portion of that transmitter; i Figure 3 represents a transposing element in accordance with the present invention; y Figure 4 represents a receiver embodying the present invention;

Figure 5 represents another embodiment of the transposing element;

Figure 6 represents a further modification of a portion of the transmitter of Figures l and 2; and Y Figure 7 represents a transposing element which may be used in connection with the arrangement of Figure 6. `In Figure l the output of an image-converter device 10, which may be of the conventional iconoscope or image 3 ortliicontype, is amplified' in a` video amplifier 11 in conventionalA fashion and fed through a coder 12 to a mixeramplier 13. Coder 12 may be, for example, similar to that disclosed and vclaimed in copendingA application SerialiNo: 243,039; filed'August" 22, 1951, issued" August 7; 1956 asli'atent2,758,153 in the nameof Robert. Adler and` assigned to the'present assignee. Such a coder may includeV a beam-deiiection tubev having a pair of output circuits-` which may be coupled selectively to^video"ampli tier' lflas'thebeamv withinthe tube is deflected fromone. to the other of` two segmental anodes coupled to such output circuits. Onelof these circuits includes a video-delayV network so that thevideo components are delayed in timewith respect tothe synchronizing components radiated by the transmitter when the beam of the deflection tube is switched to the anode ,associated with that circuit'.- Thisswitching effect is accomplished randomly by a-signal derived-lin alfashion whichwill be described subsequently; 1 Thev output ofv mixer amplifier 13 is coupled through aA direct-current inserter 14 to a carrier-wave generator and modulator 15, the output of which is radiated from antennal; 17.

The transmitter also includes a synchronizing-signal generator 19 which supplies lineand field-synchronizing components and associated pedestal componentsto mixer 13 through connecting leads- 20. The outputV of generator 19`islalso connected to a field-sweep system 21 and to a line-sweep system 22. The output terminals of eld-sweep systemA 21 and line-sweep system 22 are connectedto fielddeflection elements 23 andline-deilection elements 24, respectively, associated with image-converting device In addition, generator 19 supplies field-drive pulses to a multivibrator 28 to produce an elongated pulse of a predetermined duration in response to each applied elddrive pulse. The output terminals of multivibrator 28 are connected to amonostable multivibrator 29 which is actuated from a normal operating condition to an abnormaloperating condition in time coincidence with the trailing edge of the output pulse of multivibrator 28, to developY an output.V pulse of a predetermined time duration'. VThe output pulse from multivibrator 29 is, in turn, appliedas a gating' signal to a normally-closed gate circuit 26.

Line-drive pulses from generator 19 are supplied to a delayA line 25, the output terminals of which are connected to the input terminals of gate circuit 26 and, in addition, are connected to the input terminals of another normally-closed gate circuit 32. The output terminals of gate circuit 26 are connected directly to a generator 47. In addition, gate circuit 26 is coupled through a delay line 27 to another monostable multivibrator 31 and, by way of conductor 34, to synchronizing-signal generator 19. The output terminals of multivibrator 31 are connected to the input terminals of gate circuit 32 to provide a gating signal for that circuit. The output signal from gating circuit 32 is, in turn, applied to synchronizingsignal generator 19 over conductor 34. That conductor is also connected to the control grid of a beam-deflection device 38 to control the electron beam therein.

Beam-deliection device 38 includes a pair of deflection elements 36, 37 which are connected to the output terminals of a noise generator 35'. The instantaneous signal amplitude obtained at the output of this noise generator varies in random fashion and, when applied to the deilection electrodes 36, 37, establishes a randomly alternating beam-deflection iield within tube 38 having, at random times, an amplitude suicient to sweep the electron beam', if existent'at that instant, across a family of anode segments 40a through 40j at a rate corresponding tol the instantaneous frequency of the noise signal from generator 35.

The load circuits for the several segmental anodes 49a through 40f are completed through respective control circuits of a series of primary signal generators 41 through 4 46, respectively. The output signals from the respective anodes of beam-deflection device 38 activate associated ones of the primary signal generators in coincidence with the impingement of the electron beam in device 38 upon the associated anode segment. Each of the generators 41 through 47 is constructed in a fashion similar to that of a blocking oscillator sothat the duration of its output after the application of eachtriggering signal is selfdetermined and'A is less'than the time separation of successive line-synchronizing pulses. Moreover, each of the generators 41 through 47 has a distinctive predetermined operating frequency, as indicated by the indiciaf1 through f7 applied thereto inFigure l, to facilitate separation of the output i of each generator'fromV that ofthe others.

The respective areas of the segmented anodes of device 38 are designed so that each receives the same average current as the electron beam scans the anodes under the control of the noise signal applied to deflection elements 36, 37.

' The output terminals of generators 41 through 47 are connected to a pair of input terminals of mixer-amplifier 13.

The'burstsofenergyv at the-various frequencies, constitute coding infomation and are impressed upon` the radiated carrierfwave through mixer 13. They are impressed as downward: modulationon the verticalblanking pulse and occur lbetween the line drive pulses.

In addition the generators are coupled by Vmeans'of a conductor A and a ground' connection to the apparatus of Figure 2 and, in particular, to the primary input elements 200V through 209 and 250 of a transposer 210.A In-theabsence of avphysically'fremovableV transposing: element or panell member 211, the' primary input elements 200 through 209' and' 250' are coupled to secondary input elements 212 through 220 and 251,*respectively. The secondary input elementsy are tuned' by condensers 221: through 229'and'k 252, respectively to predeterminedl frequencies, certain of which may differ by known amounts from the operating frequencies f1 through f7 of the primary signal generators. The output signals fromthe secondary inputelem'ents are rectified by diodes 230:--238 and 253, and such rectifiedy signals are coupled to preselected ones of three Vloadfcircuits 239, 240 and 241; The output-l signals from these load circuits are coupled through unidirectional control diodes 242, 243, 244',.and 245i to the 'control` grids'- of two electron-discharge devices 246 and 247 con-nected as a controlled. bistable multivibrator 248; VThe 'anode of electron-discharge device 247 is connected through conductor B and ground` line B to coder 12 of Figure 1- Vto apply a` deection-controlsig nal thereto and effect actuation of thatcoder.

Coding iseffected in the following manner:` Periodic line-drive pulses aresupplied to delay line 25l to produce delayed line-drive pulses. The amount 4of delay introduced' is! greater than the' duration of a line-drive pulse but substantially less than the time separation. of' successive ones of such pulses. Moreover, periodically recurringfield-drive pulses are applied tomultivibrator 28. The leading edgeof van applied field-drive pulse actuates the multivibrator from its norm-al or first operating condition' to itsl 'abnormal or second operating condition and, after Va selected time interval determined. by its internal cycling circuits, the circuit returns to its first condition producing: `a pulse of energy. The parameters of the multivibrator are 'so chosen that thetrailing edge of this pulse. occurs during: theeld-retrace time of the system, at a point' following the equalizing pulses which succeed the serrated -field-drive pulse in present-day practice. This pulsal is' applied to' mono-stable multivibrator 29" which responds to the trailingV edge thereof and produces a gating pulse. The' parameters of multivibrator 29 are so chos'enrthat the gating pulse overlaps, in point of time, one pulse from-,delay line 25'. Gate circuit 26 receives the gating pulsel as well as delayed line-driveV pulses from 'delay line 2 5 and responds to their coincident'effect to a delayed line-drive pulse'to generator .V This generator is energized by the applied pulseand develops a burst of signal of frequency f7 having a time duration exceeding the duration of the actuating pulse but less than the time separation of successive line-synchronizing pulses. This signal burst of frequency f7 producedat the output terminals of unit 47 is foi-.reset purposes to be considered more particularly hereinafter.

'I'he output signalfrom gate circuit 26 isfurther de- V-layedin delay line 27 which is terminated'in its characteristic impedance yand which exhibits such a delay that to be employed in'coding-six for thc case in question.

Delayed lin-drive'pulsesA are continuously supplied from delayline 25 tol lgatecircuit 32 and those which occur within the duration of the 4gating pulse are translated to the input electrodes of beam-deflection device 38. These translated pulses intensity modulate the beam, gating it on for'theduration of each such pulse. At the same time, the variable amplitude sweep signal impressed on deflection elements 36, 37 by noise generator 35 creates a deiiection field varying at a random rate to scan the beam back and forth across segmental anodes 40a-40f. If the electron-beam `happens `to impinge on an anode segment at the instant a gated pulse is applied to the control electrode, a pulse of current'iows in the circuit of that segmental .anode to turn on the one of generators 41-46 that is coupled thereto.' For purposes of illustration it willy be-assumed that at the time of the first v pulse the beam is incident upon anode 40e Iand thus generator 43 produces a burst of signal of frequency f3. It will further be assumed that as succeeding pulses occur,

generators 42, 46, 41, V44 and 42, are turned on in the recited order, producing correspondingb'urstsof signal at i frequencies f2, f6, f1, f4'and f2. A code combination comprising a series of random but sequential primary signal of various frequencies is thus generated.

' proximately to the frequency of Ya burst of energy lfrom Vsignal generators 41-47. Each secondary element may .be tuned to the operating frequency o-f one of the generators, even in the absence of panel member or transprimary signal generators. The secondary element 213- 224 is resonant at frequency f4; secondary element 216- posingelement` 211. Alternatively, in the absence of transposing element 211 selected ones vof the secondary elements may be tuned to a frequency higher than the highest frequencyappearing in 'the aforementioned combination of bursts of energy. One function which may then be performed by the vinsertion of transposing element 211 into coupling relation with the secondary elcments is the addition of capacitance in shunt relation to existing capacitance o'f a chosen secondary element, with a. resultant reduction in the resonant frequency of that circuit to one of the preselected frequencies appearing in the combination of energy bursts delivered by signal generators. The exact fashion in which this is accomplished will be explained in detail in connection .with Figure 3;

' `The operating condition in which transposing element 211 is not functionally inserted between the primary elements and the secondary elements of unit 210 may be considered for the moment as the normal condition. For the purpose of analysing the operation of the transposing and coding circuits under this condition the following assumptions will be made. The resonant frequency of secondary element 212-221 exceeds the highest signal frequency of the combination of signals supplied by the 225 is resonant at frequency f4; secondary element 21,7'- 226 is resonant yat frequency f5; secondary element 218- 227 is resonant at frequency f5; secondary element 219- 228 is resonant at frequency f6; secondary element 220- 229 isresonant at frequency f3; and secondary element 251-252 is resonant at frequency f7. It will be further assumed that the priamry signal generators 41-47 are actuated by pulses from beam-deilection device 38 to generate the following combination of primary signal frequencies: f7, f3, f2, f4, f5, f6 and f1. Also, consider that in the reference operating condition of multivibrator 248, electron-discharge device 247 is non-conductive while tube device 246 is highly conductive; and further that at the beginning of the combination of signal frequencies the multivibrator is in its alternate stable condition in which onlyr tube 247 Vis conductive. The initial burst of energy of frequency fq'fafter selection by selector V251- 252 and rectification by diode 253, produces a negative pulse at grid 249 of electron-discharge device 2 47 and biases it to cut-olf, thus switching electron-dischange device 246 to a conductive condition; `This returns the apparatus to its reference voperating condition. Had the multivibrator been in its reference condition onthe occurrence of the frequency burst f7 the pulse appliedto grid '249 would have had no elect. Consequently, the code actuating mechanism 248 is certain to be lplaced in a reference condition at the beginning of each combination of primary signal pulses introduced by the burst of signal frequency f7 and the period in which the combination occurs may, for convenience, be called a mode-determining interval.V Y

The burst of signal frequency f3, which for the illustrative example under consideration follows immediately upon the reset frequency burst f7, is selected by selector 214-223 and rectied by diode 232 to produce negative pulses simultaneously on grid 254 andgrid 249 of electron-discharge devices Y 246 and 247, respectively. These pulses cut ofl electron-discharge device 246 and cause device 247 to'be conductive thus shifting multivibrator 248 to its alternate operating condition. While the burst of signal frequency'fa is also selected at secondary 220-229 and rectified by diode 238 to apply `a negative pulse to grid 249 of tube 247, its effect may be neglected since that tube is cut oif at the time the pulse is applied. The next burst of signal frequency f2 is 'separated by selector 213-222 -and rectified in diode 231 producing a negative pulse on grid 249 of electron-discharge device 247. Thus tube '247 becomes non-conductiveand-tube 246 becomes conductive; in other words the multivibrator shiftsto its reference condition. The succeeding burst of signal frequency f4 is selected by selectors 21S-224 and 216-225, rectied by diodes 233 and 234 and produces negative pulses both grids 2S4 and 249 with the effect of switching .on electron-discharge device 247, switching off electron-discharge device 246 and shifting circuit 248 to its alternate operating condition. When the burst of signal frequency f5 occurs it is selected lby secondaries Y 217-226 and 218-227 and Vrectiedby diodes 23S and 236. The significant control pulse -whichv results is a negative pulse at grid 249 of electron-discharge device 247. This Vreturns the multivibratorronce, again toits reference condition. When the burst of signal frequency f6 occurs it is selected by secondary 219-228 and rectified by diode 237 and appears as a negative pulse at grid 249 of electron-discharge device 247 but Vhas no effect upon the multivibrator because that electron-discharge device is already in a cut-off condition. The final burst of signal frequency f1 of the combination under consideration likewise Yhas no effect upon the system because none of the secondary selectors is Yresonant at this frequency for the assumed conditions. Y

Thus, ,the combination of; primary signals, insoover conductors B, B to coder l12 of Figure 1. This signal has a maximum amplitude when tube 247 is non- `conductive and a minimum` amplitude when that tube conducts. multivibrator is switched from .one to the other of its stable operating conditions.

It shifts between such amplitude levels as the The resulting amplitude excursions of the deection-control signal deflect the beam withincoder 12 between its two possible positions and thus :shift the operating mode ofthe transmitter between its twocorresponding modes. The operating mode established. at. the `end of the mode-determining. interval ,Y prevails untilthe start of the next such interval in which the mode may be changedlagain. far described, except forftheparticulars ofy transposer f 210 is disclosed and claimed in application Serial No.

The system as thus 326,107 led December 15, 1 952, in the name of Jack E. Bridges and assigned tothepresent assignee.

In accordance with one feature of the present invention, the displaceable component 211 of transposer 210 may be y-functionally inserted into coupling relation with the primary and/or secondary elements to vary the effect a combination of primary signals, applied during any mode-determining interval, may otherwise have on the mode changes of the system. More particularly, p-anel g member 211 by changing the coupling relationship between the primary'input elements and the secondary inputyelements or by changing the resonant frequency of one or more of the secondary selectors may vary the effect of a burst of energy-of a particular frequency on thefoperating condition of' multivibrator. 248 and the operating mode of the system. In Figure 3 there is represented; schematically a transposing element 211 for alteringy the circuit relationship between the primary elements and the secondary elements of unit 210 and for transposing the bursts .of primary signal energy from the Vstandpoint of their lselective application to they severalv inputcircuits ofmultivibrator 248. As illustrated, transposing element 211 comprises a printed condenser 300 having oneelectrode 301 connected to a terminal 302 and another electrode 303, `printed on the opposite vside of a supporting member of dielectric material and coupled to a ground lead 304. Terminals 305, 313, 314,

I317..and 370 may, in this embodiment, be dummies.

Terminal 306 may-connect toA one electrode 307 of a second condenser-308, the opposite electrode of which is connected by means of conductive strip 309 to a terminal 310. Ay shielding element 311, which is grounded,

may be provided on one side of the support member while on the opposite side thereof a coupling link 312 may be printed; its contour and physical position on the support are so chosen'that when the transposer is in its operating-position this link overlaps adjacent and preselected primary input elements. Terminal 315 connects toy one electrode of still another condenser 316 f having. its other electrode grounded. Ground strip l304 .is connected to terminal 318 and a shielding element 319 is placed adjacent terminal 310 andV grounded to terminal 318. Whilerthe components on transposing elevment 2,11 have been described as printed they may be Y the conventional variety. AV top and/or` bottom cover of insulating material (not shown) may be placed over the described structure to form alaminated component on theouter surface-of which appear only terminals corresponding to terminals 302 through 318 and 370. Of course,..the parts of this structure may, if desired, be printed on a highf dielectric sub-base which is then .encased in some insulating material.

When the described transposing .element 211 is func- ,tionally inserted intounit 210 of Figure 2iterminals302, 305, 306, 313, 314,315, 317, 370 and'310fengagecontacts 270 through 278, respectively while .terminalA 318 engages contact 280. The condenser 300 `of element 211 has such a capacitance 4that when itshunts. condenser 221 through mating contacts-302-270 .and .318-280..the secondary element comprising inductor 212 .resonatesat frequency f1. Mating contacts 306-272,and 310-278 connectlcoupling condenser 307 between thehighl potential terminals of secondary element. 214-223v .and secondary elementv 220-229.. At the same time; primary input element 209 is isolated or shielded from secondary element 220-229 by shield 319.0f transposing element 211. Moreover, coupling link 312 of the'transposing element inductively couples secondary element 21S-224 -to secondary element 216-225 while shield 311 prevents energy in primaryinput element 203 from being coupled to secondary element 2115-224. Mating contacts 315-275 and,318-280 connect condenser 316 in-shunt relation to condenser 226. and change ,the tuning of the secondary element comprising'inductor. 217 ffrom normal frequency f5 to frequency f4. No yother. circuit transpositions are effected upon the insertion'of lthe element of Figure 3 into functional relation-,with Vtransposer 310.V

With transposing elementv 211 in operating position the effect of theaforementioned combinationof bursts of signal energy delivered by signalV generators 41through 47 (namely, signal frequencies inthe order fr, f3, f2," f4, f5, f6 vanclv f1) is as follows. Multivibrator 248, if it is not in its reference condition at the start of thecombination is reset in response to the burst of signal frequency f7 inthe fashion previously described. The burstof signal frequency f3 is selected by secondary 214-223, rectifed'indiode 232 and impressed with negative polarity upon grid 254 of electron-discharge, device 246. Simultaneously, by reason ofv the capacitive coupling through condenser 308 carried vby element 211 the signal burst also appears across secondary element 220-229 even though that element is shielded from its associated primary 209 by shield 319 of device 211.' The Vsignalfis rectified by diode 238 and produces a negative pulse on the grid 249 of electron-discharge` device 247. .'The pulses thus produced cause a switching action in the lmultivibrator; electron-discharge device 247 becomes conductive while device 246 is cut off. The nextburst of signal energy occurs at frequencyfz. It is 'selected by secondary 213-222 and rectified by diode 231 which produces arnegative pulse at the grid 249 of *electrondischarge device 247, thus cutting off thatl tube and returning the multivibrator to its initial or reference condition.

The following burst of signal energy occurs at frequency f., and is selected by secondary element I216-226. The coupling link 312 couples this .energy into Vsecondary 21S-224 which is otherwise shielded fromits primary element 203 by shield 311 of* device 211.y Consequently,

rectified pulses appear atY the output of. both diodes233 and 234 yand hence on both grids 254 and 249 .of the electron-discharge devices in multivibratory 248 simultaneously. At the same time secondary element 217-226 selects the burst of signal energy which. is then rectified in diode 235. The overall effect ofy these'pulses thus applied to theinput circuits of tubes 246.and 247 is to switch `the multivibrator once more from its -reference toits alternate operating condition.

The next burst of signal energy occurs at frequency f5 and is selected by secondary element 218-227. It is rectified by diode 236 and appears at both grids 254.and 249 to trigger the multivibrator, from its instantaneous condition to its alternate condition. Then a burst of signal energy at frequency f6 is selected by secondary element 219-228, is rectified by diode 237 and develops a negative pulse on grid 249 of electron-discharge ldevice 247. This signal hasv no effect onthe multivibrator .5379 since device 247 is' already in its non-conductive state. The burst of signal energy of frequency f1 is selected by secondary Velement 212--221, rectilied by diode 230, and

applied to grids 254 and 249 of the multivibrator which is switched thereby to its operating condition in which electron-discharge device 246 is non-conducting and electron-discharge device 247 is conducting. y

y Thus, it -may be seen that the introduction of transposing element 211 into functional relation Within unit 210 causes the illustrative combination of primary signals to have a different eifect on multivibrator 248 than otherwise. This results in a modification of the deection controlsignal delivered to coder 12 and changes the coding pattern of the transmitter. More particularly, panel member 211 by adding reactive impedances into -selected ones of the second-ary elements and/ or by changing the coupling relationY between them modifies the effect a burst of signal energy of any particular frequency may have on the system. The transposing element 211 is freelyireplaceable and facilitates the changing of code patterns from time to time to minimize the possibility of unauthorized appropriation of the subscription television program. Elements 211mayr be distributed to subscribers in any Aconvenient manner as by mailing, by vending machines or through distribution centers.

element 419 substantially identical with transposing element 211 employed at the transmitter. If replaceable transposing element 419 be neglected for the moment, this receiver is the same in all material respects as the receiver of the aforementioned Bridges application and, assuming theY replaceable element 211 is not employed in the transmitter, it Vfunctions in a generally similar manner to develop a deflection-control signal for application to de- Vcoder 415. When the replaceable transposer is taken into consideration, the receiver operation is modified in precisely the same manner as the insertion of the corresponding replaceable element modifies the coding schedule or pattern of the transmitter of Figure l hereof. Consequently, the combination of signal bursts of frequencies f1 to f7 controls bistable multivibrator 414 to develop a deection-control signal which actuates decoder 415 in Va complementary sense to the actuation of coder 12 at the transmitter as required to decode the telecast and effect image reproduction on the screen of kinescope 470.

It may be particularly desirable in practicing the present invention to construct the replaceable transposing ele- Vment of the transposer units in such manner that it has The arrangement under consideration is very exible in that any of a number of circuit transpositionsis possible, depending upon the construction of transposing element 211. A secondary element maybe tunedto a lower frequency by adding capacitance thereto, may be capacitively coupled to another secondary element by a coupling condensercarried on theV transposing element,

.may be inductively coupled to another lsecondary element the subscription telecast originating at the transmitter of Figures l and 2. It comprises an antenna 410 coupled to the input circuit of a radio-frequency ampliier 420. The receiver further comprises .a first detector 430, an

' intermediate-frequency*amplier 440, a second detector 450,` a video amplier 460,` an imageY reproducer 470, a synchronizing-signal separator 480, a horizontal sweep system`490 and a vertical sweep vsystem 495. The components are of. well-known construction -and'operate in conventional manner in the reproduction of an image.

` A decoder 415, similar to coder 12 of the trasmitter of= Figure l, is included between the video amplifier and image reproducer. It is actuated in response to a delec` tion-control signal from a bistable multivibrator 414 which corresponds to multivibrator 248 of Figure l although the actuation of decoder '415is in anoppposite sense to that of coder 12 at the transmitter. This results in compensation Vof the coding produced at the transmitter andthe reproduction of an image on kinescope 470.

The bursts of signal energy at frequencies f1 through f7, employed for coding purposes at the transmitter and radiated along with the subscription telecast, are removed from the vertical blanking pulse of the received signal by a gated amplifier 416 which is coupled -to second detector 450. The gating signal for activating amplifier 416 is derived from a mono-stable multivibrator 417;"

which is controlled by vertical synchronizing pulses from separator 480. Thesignal bursts so removed are applied to the primary input elementsof a transposer 418, which is substantially identical with 4transposer 210 of Figure 2 and arranged-to accommodate a replaceabletransp'osng no external terminals which may be significant to unauthorized persons attempting to decipher the electrical specications of the replaceable element. A construction of the element employing no external terminals is represented in Figure 5 where, for convenience of illustration, the exterior covering has been broken away to reveal the circuitry of the device. In this form, the device comprises a supporting card or stripof insulating material upon which is imprinted two elongated conducto'rs 500 and 501. A series of coupling loops 502- 508 are abridged between these conductors; the number of loops employed is dictated by the particular arrangement ofthe transposer with which the replaceable element is to be employed. For that reason, conductors 500 and 501 have been represented as discontinuous to indi- Y cate that there may be moreloops interposed between the conductors than actually represented in the drawing.

The space relation of the loops along the insulating support is determined by the space relation of the secondary elements of the transposer with which the card is to be associated. When the element of Figure 5 is functionally inserted into a transposing unit, such as unit 210 of Figure 2, the series of conductive loops supported by that element are to have such relation to the secondaries of unit 210 as required for effective coupling of each'loop to the inductor of an assigned secondary element of unit 210.

This embodiment of the replaceable transposing element is most effective when the transposer unit employs a single primary input element, such as that designated 200 in Figure V2, in addition to the primary element 250 utilized for reset purposes. The other primaries 201-'209, inclusive, are omitted and, preferably, primary 200 is shielded or otherwise decoupled from the series of secondaries; When the replaceable element is functionally introduced Iinto such a transposing unit, the rst coupling loop 502 is inductively coupled with the primary input 200 and the transfer of signal energy to the secondary elements is under the control of the circuitry of the replaceable element. Where any succeeding coupling loop v of the replaceable element, such as loop 503, `is conductively connected with conductors 500-501 signal energy introduced into the rst coupling loop 502 from primary 200 is translated through the closed circuit including loops v 502 and 503. As a consequence, this signal energy is then transferred inductively from coupling loop- 503 to its associated secondary, for example secondary 213- 222 of Figure 2. Energy transfer in similar fashion oecurs-to all of the secondaries for which the associated coupling loop on the replaceable element is effectively in circuit with the loop 502 driven by the primary input for loops 503, 505, 507 and 508.

I@ Where any-flopp ofthe replaceable element is eiectiveilytdisassociiatedvcircuitwise from conductors 500and 501, there isffno Acoupling through that loop to itszassociated secondary element-and, therefore, no transfer of energy ,takes place from the primary 200 to such secondary. In ..l.-.thefarrangementillustrated, loops 504 and 506 are repren-sented schematicallyatpoints 516 and`517as electrically `.fdisassociated#with conductor strips-'500and 501.v This v-may be accomplished, of course, by omitting vor breaking -rttheconnector.- which otherwise is employed to complete etheloorinection `from those conductors to the coupling -:-..loop',:orv alternatively, ithe loops themselves may be omit- @ted inthezconstruction of the replaceable transposing eleaiment.

til-his rtransposingelement is diicult to pirate because .''thetcircuit components; thereof are completely encased within:a:laminated structure Vwhich presents no terminal information f- The -transposing unit is subjected to circuit .rtmodiiications ,bylathefintroduction of this replaceable elezment: into functional relation' therewith; the replaceable @elementi determines which of theA secondary elements of :r-theftransposing-unit is Veffectively coupled to the driver --prim-ary element 200and the effectiveness of the coupling s. is selectively controlled bythe tuning or selective proper- .nrtiesrofithe secondaries. The response of the bistable mul- '..xtivibratonincluded'within the transposing unit to a comfbination '.of .signal pulses of different frequencies applied @ttor-primary `200 isf generally similar to that described in erconneetion with the .operation of thedevicefepresented :gineligures 1,` 2` and 3, differing primarily in the manner I :in which signal energy is transferred Vfrom the single primary -to the series of secondaries.

In cert-ain embodiments of the present invention, the :..ereplaceableelement of the transposing unit may advanwtageolusly.` be lemployed in a system wherein the code vxinformation is represented, at least in part, by combina- .l.tions ofwbursts olf signal energy subject, fromv time to .-..-time, -to frequency modulation. The additional step of -introducing frequency modulation in respect of the combinationy of primary signals makes it difficult for unau- -1 thorized persons to appropriate the subscription telecast by f'ftbreaking the code that has been employed. An arrangef-mentofi the type under consideration is represented in #Figure 6 whichzshows, schematically and in modified form,

iwonly; so `much'ofthe transmitter of Figures 1 and 2 asv- 4 concerns the, generation of the combination of primary ;signals and the application of those signals to input termi- .nals ofthebi-stable multivibrator which develops the deflection-control signal for the coding device 12.

More specifically, a noise generator 600 develops a'.60

f balanced deflection signal for deflection electrodes 601 pand602 of a deflection tube 603. This tube'is reprel sented as having only three segmental anodes 604a, 60411 wand .604e although Vthe number to be employed is, of course, determined by the number of signal components lto be included in the combination of primary signals utilized in a mode-determining interval to ascertain the operating mode to be imposed on the transmitter until the `occurrence of the next such interval. Each anode seg- .ment isy coupled to an assigned one of the primary signal generators 605,1606 and 607 through a modulating de- .vice here represented as reactance tubes .60511, 606er. and i 607a. It ispreferredzthat each reactance tube arrangement include its own cycling circuit so that a current pulse applied to the modulating device from its assignedy anode segment of deflection tube 603 renders the reactance tube effective for apulse interval` which iat least vcorresponds tothe pulse intervals of the individual primary signal generators.

The pulsed operation of the primary signal generators.:

is Aunder thecontrol of a similar deection tube .603:1 to which a deflection control signal is applied from a` second noisegenerator 60011. The anode-segments of this lastmentioned deflection tube :are .directly coupled .tothe :i112 cycling circuits. tof.` the primary signalfegeneratorsinhe .mannerofFigure 1.

In `the embodiment. of Figure. 6, the output circuits of the primary signal. generators are coupledto thetransposer unit-610, the output circuitsof such generators being connected to a source of operating potential; lrepresented as a battery 611,*through series-connectedy primary ele- .-n1.ents612,y .613 and` 614. Thesecondary elements of the `.t transposer are groupedvin pairs to constitutea multiplicity :.off frequency modulation discriminator-detectors for respending to the frequency modulation imposed on the primaryisignals. Three such detectors have been represented--sincethe transmitter, for thel case inquestion, has -beenshown asY includingonly three primary signal gen- -15.=erators. 4

The iirst such detector includes the usual pair of diodes 615 andY 616 .havingresistance-capacitance load circuits .-..617and-6;18. The circuit lof onel diode, when condiitioned fordetection, istuned toa frequency whichzis -fhigher than. la` reference -orzfnominal frequency bysome incremental value Whereas the circuit of the other diode, .for the samek conditions, istuned to a lower value than the mean..frequency by the same increment. This tuning -maybetaccomplished for diode 615 by means 'of an in- I22.5 ductor ,-619 and capacitive reactance including a condenser t6.20,;1the,corresponding.components of vthe-.circuit of the t alternatendiodel are designated 621 and 622.*V The .circuit connectionsof the condensers 620 and 622 with .l respectto the. secondaryinductors 619 and 621 are tobe V30...corr1pleted,....ifat.- all,through mating contacts of the de- .tector ..circuitand.of areplaceable transposing element 4 .700. jIhereare tive contact pairs for. each detector.

`,The..stationary..contacts, which areY permanently in- ...tegrated in the detector. circuit, are as follows: 35,v Contact 626 which is connected to the junction of one .terminal of.condenser.6l20 and one terminal of inductor .619; contact..624 which. connects to the opposite terminal of condenser 620; contact 625 .connected vto the junction of inductors 6119 and.6121;.contact 626 connected to one terminal ofconde'nserr 6-22; and contact 627 connected tothe alternate terminalofthecondenser and its junction with .inductor .621.' AThemating contacts, which ....mate.with:.the.stationaryones.in the order recited, are ...designated 701-705,. inclusive, and they are .carriedV by rfthe.replaceable.element 700 to be .considered..more parlticularly presently.

' ikThe second .detector circuit includes inductors 630 and .631as .well asftuningcondensers 632 and .633 which are v.cormected tol the samearrangementof stationary conftactsf..And. the` third detector comprises inductors'634 .and 6352s- .welL'as `tuning Ac0ndensers'636 Vand 637 also ,".fconnect'ed -tothesamearrangement of stationary contacts'. "'The. tunedy input'circuits ofthe several detectors .'canbe completed-bythe. circuitry of the replaceable 55W`el'ement1700 `which-may provide for-a variety ofy circuit connections as iiidicated in' Figure' 7.

j In thatgure it is apparentltha't the .replaceable .ele- 'lmen't has `as many groups of contacts as there. are detecft'ors, 'th're for the specific embodiment represented. Each ."xeodfsuch group comprisestive contactsv 700%705. '.Inthe Aiirstconta'ct group, the middle'three contacts are conductively connectedin series and no connections are made Vtothe end 4contacts.k n

l 'LThe 'next Contact;` group 'of replaceable 'element'. 700

has beenjdes'igriatedfby theieference characters V701i:-

705a,'hinclsive. 'Associated with the contacts of this ,Y group, are a' pair of-condensers`706-and 707 which are Yr'rrintedronlreplaceable. element'700. The mechanics 'fof 'constructingthe condensers yonthe element are well ,miunderstob-invgeneral, the replaceable. element may comj...prisefa.'suppofrting .member Aof .insulating dielectric maf. .terial andwonefele'ctrode ofeach condenser is Vprinted on one sideV ofthe. dielectric while theopposite electrode "ofeachicondenseris printed ori-...the other side in space .rlatipnto. -its...co mpan ion .electrode One., electrode. .of

condenser 706 is connected to contact 701:1 and -its other electrode is connected to contact 703m One electrode -of condenser 707 is connected to contact 703a and its otherv electrode is connected to contact 704e. Contacts 702:1 and 703:1 are conductively connected while contact 705a serves as a dummy. Y i

YVThe final contact group, represented by reference numerals 7015-7051:, inclusive, shows still a further arrangement for completing the input circuitsof the FM detectors.. This also involves the use of printed condensers 708 and 709 carried on the replaceable element "700. One electrode of condenser 708 is connected with Y contact 701b, its other electrode being connected to "contact 703b. One electrode of condenser 709 is connectedto contact 70512 and its other electrode is connected to contact 70317. Contacts 702b and 7 04b may be considered as dummies.

' The -modiiied Vstructure of Figure 6 may Ibe incorporatedinto the transmitter ofFigures 1 and 2 in place ofY thenoise 'generator 35, deilection tube 38, primary generators 41-47 and transposer 210.V When the substitumals `has no eiect because thefinput circuits .vof-the tector diodes are incomplete inthe absence ofthatelement. On theother hand, in the presenceof thev replaceableelement the effect ofthe given combination of pri- Vmary signals is determined by the circuitry or speciiications of that element. For example, with the illustrative replaceable element of Figure f7 thetrst'contact @group 701-705 merely couplescondensers 620 and 621 in parallel with the secondaryV inductors` 619 and- 621,

respectively. Assuming that the inductors and condensers of detector 615-616 have equal values, lthis detector is not responsive to the combinationof primary signals because the input circuit of diode 615'A is then tuned to the same frequency as the input circuit of diode 616 and theoutput voltagesdevelopedin their load cirg ,cuits cancel and annul one another.

The middle contact group 701a-705ay of Ireplaceable element 700, on the other hand, causes inductor 630 to tion is made, the control electrodes of deflection tubes 603 and 603a`of Figure 6 are connected to the output terminals VOftgate circuit 32,1the output terminals of primary generators 605-607 which terminate in the arrows ofFigure 6 are connected to mixer amplifier 13; the output terminals 640, 641 andV 642 of transposer 610 may be connected, respectively, to the junction of the cathodes of diodes `242 'andA 243 of Figure 2, to the cathode of A diode 244 land to the cathode of diode `245 so that the bi-stable multivibrator 240 is actuated by the modified transposer 610 in place of transposer 210 of Figure 2 to develop a deectioncontrol signal for application to coder 12.

" In operating the modified structure of Figure 6, the nominal operating frequencies' of primary generators 605-607 are chosen so that there is no interference or overlapping of the significant frequency range of any such primary generator with any of the others of the group. This merely' requiresl adequate separation of their operating frequencies. The effect of dellection control tube 603a in energizing the primary signal generators in a random sequenceis precisely as described in connection with the arrangement of Figure 1' so that in any mode-determining interval any Vsuch generator may be energized and the order of their energization Vmay be i changed in random manner under controlof noise generator 600a. In like fashion, ydeflection control tube 603 in conjunction with noise generator 600 keys the reactance tubes 605a to 60711 in random manner so that any par- 'ticular yreactance tube may orA may not be energized t in any given mode-determining interval.

As a consequence, in any such mode-determining interval there may be a combination of primary signals de- .veloped by generators 605-607. If in a particular interval, :generator 605 is operated and if its reactance tube '605:1 has not been ,energized at the sam'e time, the

. burst yof signal energy for `the particular instant is of the frequency f1, the nominal operating frequency of the generator. On the other hand, should'the reactance tube `be concurrently energized, the burst of signal energy is then at a frequency f1 plus `Af or fi minus Af, where Af .isr a change in frequency imposed by-the reactance tube in a sense to increase and decrease the nominal frequency f1 in accordance with the characteristics of the reactance tube and the sense of the reactance which it simulates,

as iswell understood in the art. Hence, in each modedetermining interval `a combination of primary signals maybe generated'variously representing the mean operating `frequency of the primary' generators or such frequenciesmodiiiied by the effects of the reactance tubes.` This combination of primary signals is applied to the I primary elements of transposer 610.

. Until 'the replaceable element 700 of the transposer l his, inserted into-place,- such combination of primary sig element.

be ltuned by condenser 632 in parallel -with condenser -70'6V carried by the replaceable element'.V .At thesame time, inductor 631 is ,tuned by condenser r633 in series with condenser 707 likevvise carried .on the replaceable ByY appropriate selection. of condensers4 706 and 707'oneof the diodes of this detector is tuned. to

of the primary generators, such asgenerator 606, wherethe lnominal operating frequency of anyv particular one as the companion diode of that detector is tuned to the operating frequency of that samegenerator as modied by its reactance tube 606:1. Consequently, any signal component of the combination of primary signal having a frequency f2 produces an output pulse at terminal 641 of this detector of one polarity where as any signal energy of the frequency f2 plus (or minus) Af produces an output pulse at the same terminal but of opposite polarity.

The final contact group included in replaceable ele- 4ment 700 leaves the circuits of condensersV 636 and 637 open and tunes secondary inductors 634 and 635 Wholly by condensers 708` and 709 carried on the replaceable element. Preferably, they tune one diode of this detector to the nominal operating frequency of a chosen one of the primary signal generators and tune the companion diode to themodiied operating frequency of the same generator when its reactancetube or modulator is eiective. The tuninlg of this detector results in an output pulse at terminal 642 of positive or negative polarity depending upon the presence in the combinationof Yprij mary signals of components occurringat the nominal operating frequency of the selected generator or at its modifiedrfrequency.

The pulses thus made available at output terminal 640, 641 and 642 of transposer 610 may be employed to effect a determination of mode on the basis of bipolarity code information or, as in'the embodiment shown, they may be selected on the basis of polarity and utilized after that selection to actuate multivibrator 248 of Figure 2. The diodes 242, 243, 244, and 245 `through which the output terminals of transposer- 610 connect to the multivibrator respond to pulses of negative polarity but not to pulses of positive polarity and, therefore, introduce ar selection of pulses on the basis of polarity. VThe actuation of the multivibrator develops a t unauthorized user to break the coding arrangement of the system. If desired, the several detectors of transposer 610 may, in the absence'of replaceable'element 700,

..be..tuned so..that the. diode of .one detector responds to ,..thenominahoperating frequency of a primary generator vmaychangexthe tuning sok that both diodes inthe pres- .enceof .the card are tuned' to the same frequency which --theneiectively disables that detector. Alternatively, it Y .mayreverse thel conditionsof tuning to change'thetuning ofthe diode previously responsive to the nominal-.operatv ing* frequency of the selected primary generator to the modified operating frequency of the same generator and Avice versa. A changeof this type inverts the polarity of the pulses otherwise obtained at the associated output terminal of that detector.

It has been convenient in the representation of Figure 6 .tofomit the .counterpart of the .reset'generator 47 ...usually andpreferably included. in the transmitter. MIt, ofcourse, may-be added to the arrangement of Figure 6 Las a.substantialY duplication .of the reset arrangement in- ..,.cluded in Figures l and 2. l

` ..Thus,.this invention has provided a subscription television system which assures maximum freedom from .pirating With a minimum of complexity andcost. YFur- ..th`e"r, the transposing element described herein possesses the desirable features of ease of merchandizingrand fIee- .dom from easy duplication. :fWe claim: u

1. Inv a-subscription televisionv system: anencoding mechanism having a plurality of `operating conditions .Y veach of which imposes a different ,operating'mvode upon saidvsystem and responsive to appliedsignals Vtoshift from one suc-h.operatingfconditionto another; means .for deriving atleast one primaryencoding signal; a

transposer coupled between said signal-deriving' means and said encoding mechanism'lfor determining the re- :sponse of said mechanism to said primary signal, .said transposerincluding at least'one primaryinput-'element .n and a plurality of secondary input elements spaced from,

`and normally having` a predetermined circuit relation` .ship with respectrto, said one primary input element for translating said primary signal Vto a predetermined jone 'of.said secondary .input elements to effect; a preselected response of said mechanismto said primary 4signal and a panel mamber insertably disposed between said primary and secondary input elements and-in functional relation-1with'respectto said transposer andcomprising eachof which imposes adiiferent operating. mode upon3g55- saldi systemand responsive to applied signalsto .shift vvfrom yone vsuch operatinglcondition to :another;.. means forderivingl at le'ast one primarysencoding signal;W a

transposer coupled between; said signal-deriving. .means .rand ,said encoding mechanism lfor determining .t'herefr @sponse of :said mechanism'to said primary. signal, said transposer including a plurality of .primary input. elements-'and a plurality ofzsecondary .inputelements normally having a: predetermined .circuit relationship `with "716 3. In a subscription television system: an encoding mechanism having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive to applied. signals to shift from one such operating condition to another; means for deriving at least one primary encoding signal; a

transposer. coupled between saidsignal-deriving means and secondary elements to modify said coupling of such Y elements so that said primary signal as translated by said transposer to said encoding mechanism establishes .-a different preselected response of said mechanism. to

said signal.

4. In a `subscription television system: an encoding mechanism having a plurality of operatingconditions each of which imposes a different operating mode upon saidl system and responsive to applied signals to shift from one such operating condition to another; means for deriving at least one primary encoding signal; a transposer couplid between said signal-deriving means and said encoding mechanism for determining the response of said mechanism to said primary signal, said transposer including a plurality of primary input elements and a plurality of secondary input elements normally having a predetermined circuit relationship with respect to one another andestablishing al preselected response of said mechanism to said primary. signal; and a transposing element removably disposed in functional relation with respect .to said transposer andcomprising reactivev couplingimpedancesinterposed between selected ones of said primary and secondary elements to effect .further couplingtherebetween so that said primary signal .as translated by said transposer to said encoding mechanism establishes a'diiferent preselected responserof said mechanismto said signal. A

5;:In a..subscription television system: an encoding .mechanism y'having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive Ato applied signals to shift from one.such operating condition to another; means for deriving at least one primary encoding signal of a .particular frequency; a transposer coupled between said signal-deriving means and said encoding mechanism for determining the response of said mechanism to said primary signal, said transposer including at least one primary input element and at least one secondary input .element spaced from, and normally having a predetermined circuit relationship With respect to, said one primary input element and establishing a preselected' response of said mechanism to said primary signal; and a panel member insertably disposed between said primary .and secondary input elements and in functional relation with respect to said transposer and comprising a reactive .impedancecoupled to one of said input elements to 1 Vrespect -to one another. for translatingsaid primary signal165 to a-predetermined oneofsaidy secondaryinp'ut elements toeifect agpreselected responseofsaid mechanismfto 'said primaryf signal; and a. .transposinglelementi-removably disposed in functionalrelation Withfrespect to said y transposer and :comprising .circuit components coupled,Vv

-ito-selected ones 'of said .primary'and secondary elements for-.modifying said .circuit :relationship -of vsuch i elements .-to .effectively translate saidA primary Asignal-.to another I.one of saidr secondary input elementsY to vary theresponsefof...said.A mechanism to said signal.

:tune said one element to a preselected frequency. and

modify the response of said mechanism to saidsignal.

6. In a subscription television system: an encoding vmechanism having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive to applied* signals to shift from one such operating condition to another; means .for deriving at least` one primary encoding signal; a

: transposer coupled between said signal-deriving means and said encoding mechanism for determining the responseof-said mechanismY to said primary signal, said .transposer including at leastY oneeprimary `input element and at least one timed secondary input element normally having a predetermined selectivity with respect to said primary signal and establishing a preselected response of said mechanism to said primary signal; and a transposing element removably disposed in functional relation with respect to said transposer and comprising a reactive impedance coupled to said tuned secondary element to vary the selectivity thereof so that said primary signal as translated by said transposer to said encoding mechanism establishes a different preselected response of said mechanism to said signal.

7. In a subscription television system: an encoding mechanism having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive to applied signals to shift from one such operating condition to another; means for deriving at least one primary encoding signal; a transposer coupled between said signal-den'ving means and said encoding mechanism for determining the response of said mechanism to said primary signal, said transposer including at least one primary input inductor and at least one secondary input inductor normally having a predetermined mutual coupling and establishing a preselected response of said mechanism to said primary signal; and a transposing element removably disposed in functional relation with respect to said transposer and comprising a shield disposed between and shielding said elements from one another to prevent eifective transfer of said primary signal from said primary to said secondary elements.

8. In a subscription television system: an encoding mechanism having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive to applied signals to shift from one such operating condition to another; means for deriving at least one primary encoding signal; a transposer coupled between said signal-deriving means and said encoding mechanism for determining the response of said mechanism to said primary signal, said transposer including a primary input element and a plurality of secondary input elements spaced from said primary input element and individually coupled to said encoding mechanism for translating said primary signal to a predetermined one of said secondary input elements to effect a preselected response of said mechanism to said primary signal; and a panel member insertably disposed between said primary and secondary input elements and in functional relation with respect to said transposer and comprising a coupling network selectively coupling said primary element to particular ones of said secondary elements to eiect transfer of said primary signal to another one of said secondary input elements to vary the response of said mechanism and determine the effective operating mode of said system.

9. In a subscription television system: an encoding mechanism having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive to applied signals to shift from one such operating condition to another; means for deriving at least one primary signal having a frequency within a given range of frequencies; a transposer coupled between said signal-deriving means and said encoding mechanism for determining the response of said mechanism to said primary signal, said transposer including at least one discriminator-detector having a preselected response to signals Within said range of frequencies; and a transposing element removably disposed in functional relation with respect to said transposer and comprising circuit components coupled to said discriminator-detector to modify the response thereof to signals within said range of frequencies so that said primary signal as translated by said transposer to said encoding mechanism establishes a preselected response of said mechanism to said signal.

l0. In a subscription television system: an encoding mechanism having a plurality of operating conditions each of which imposes a different operating mode upon said system and responsive to applied signals to shift from one such operating condition to another; means for deriving at least one primary signal having a frequency within a given range of frequencies; a transposer coupled between said signal-denving means and said encoding mechanism for determining the response of said mechanism to said primary signal, said transposer including at least one discriminator-detector; and a transposing element removably disposed in functional relation with respect to said transposer and comprising circuit components coupled to said discriminator-detector to establish a predetermined response thereof to signals within said range of frequencies so that said primary signal as translated by said transposer to said encoding mechanism establishes a preselected response of said mechanism to said signal.

References Cited in the le of this patent UNITED STATES PATENTS 2,226,508 Clothier et al Dec. 24, 1940 2,402,058 Loughren June 11, 1946 2,437,255 Hogan et al. Mar. 9, 1948 2,501,274 Hamilton Mar. 21, 1950 2,526,694 Samet Oct. 24, 1950 2,539,556 Steinberg Jan. 30, 1951 2,656,407 Herrick et al. Oct. 20, 1953 FOREIGN PATENTS 986,834 France Apr. 4, 1951 

